Retroreflectors in the form of sheeting are often used in diverse applications including projector screens, traffic signs, and safety garments for road construction workers. In each of these cases, a purpose of the retroreflector is to increase or direct the visibility of reflected light. Retroreflective sheeting can comprise a layer of transparent plastic material having a substantially smooth front surface, and a rear surface provided with a plurality of retroreflective elements. Conventional retroreflectors use these elements to reflect an angular cone of light back towards the source. The angular spread of the cone is determined by the properties of the retroreflector. The returned light typically is brighter close to the source (at smaller observation angles), and falls off farther from the source (at larger observation angles).
An example of a retroreflector can be found in International Patent Application Publication No. WO 99/15920, which describes a reflective article having a structured surface which includes a plurality of reflective elements, each having a first, second, and third mutually reflecting face with definable dihedral angles. At least one of the dihedral angles differs from a right angle by more than two degrees. In one embodiment exactly one of the dihedral angles is so characterized and the remaining dihedral angles differ from a right angle by less than two degrees. In one embodiment the reflective elements are bounded by a plurality of groove sets in the structured surface, the groove sets having a preferred groove spacing between about 0.0004 and 0.002 inches (10-50 μm). Reflective elements having different sets of dihedral angles can be incorporated in the structured surface by tiling or by providing one or more sequences of grooves with differing groove side angle pairs. The article reflects an obliquely incident beam of light into two reflected beams on opposed sides of the incident beam. One of the two beams has a beam width sufficient to illuminate a predefined observation zone angularly displaced from the incident light direction.
The cube-corner retroreflective article of U.S. Pat. No. 4,775,219 includes three lateral reflecting faces formed by three intersecting sets of parallel V-shaped grooves, with at least one of the sets including, in a repeating pattern, at least two groove side angles that differ from one another. Thereby the array of cube-corner retroreflective elements is divided into repeating sub-arrays that each comprise a plurality of cube-corner retroreflective elements in a plurality of distinctive shapes that retroreflect incident light in distinctively shaped light patterns.
The display system of U.S. Patent Application Publication No. US 2017/0160631 comprises a retro-reflective screen having retro-reflective screen elements that reflect incident light. Each of the retro-reflective screen elements can include three intersecting planes. At least one of the three intersecting planes intersects an adjacent plane at an angle that is 90 degrees with an offset greater than 0 degrees. The display system can further include at least one projector that projects the light onto the retro-reflective screen, which light characterizes an image or video. The retroreflective screen having the retro-reflective screen elements can reflect the light at a cross-talk that is decreased by at least 10% and/or an intensity that is increased by at least 5%, as compared to a retro-reflective screen with retro-reflective screen elements having planes that each intersect an adjacent plane at an angle of 90° without the offset.
Even in view of these references, the need exists for retroreflective sheeting that can be used in a projector-based display for the focused direction of reflected images to multiple viewing positions located at different positions relative to the projector.